A Review of Prey Selection by the Long-Eared Owl

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Cooper Ornithological Society is collaborating with JSTOR to digitize, preserve and extend access to The Condor. This paper describes variety and size of prey of the Long-eared Owl (Asio otus) from widespread parts of its range and develops a diet profile for the species. Compared to sympatric species, the Long-eared Owl has a restricted diet (Craighead and Craighead 1956, Errington 1932, Korschgen and Stuart 1972, Marti 1974, Maser et al. 1970). Food habits of this species have been extensively reported from North America and Europe. There are, however, large areas within its range from which no reports on diet are available. The Long-eared Owl is Holarctic in north temperate regions of North America, Europe and Asia (see Grossman and Hamlet 1964). This is a strictly nocturnal species (Marti 1974) and apparently feeds almost exclusively in open lands (Getz 1961, Randle and Austing 1952, Smeenk 1972, Weller et al. 1963). However, it does require small, dense trees for nesting and roosting (Armstrong 1958, Bent 1938, Marti 1974). This species is a medium-sized owl; mean weight of 66 specimens from North America was 262.3 g (Earhart and Johnson 1970). Several morphological adaptations point to efficiency of hunting in open areas. The long wings seem to be adapted to this habitat (Lack 1966), and compared to many other North American owls this species has rather light wing-loading, which indicates efficiency of hunting on the wing. Poole (1938) calculated wing-loading for the Long-eared Owl as 5.13 cm2 of wing area per gram of body weight for males and 4.22 for females. METHODS AND MATERIALS The analysis of prey variety and size is based on data from studies listed in table 1. Most weights WOOLLER, R. D., AND G. S. TRIGGs. 1968. Food of the Long-eared Owl in Inverness-shire. Bird Study 15:164-165.

Winter diet of the long-eared owl Asio otus (Strigiformes: Strigidae) in the grasslands of Janos, Chihuahua, Mexico

“…Cricetidae were dominant with a frequency of 54.61%, below the range reported by several authors and worldwide (88-97%), with the exception of Africa/Middle East (71.5%) and Asia (59.8%), where Muridae was the most frequently consumed rodent family [1,3,11,[15][16][17]. On the other hand, biomass percentage is consistent (80.69%) with known range of values (86-98%) [9].…”

“…Sigmodon was undoubtly the most important prey for the long-eared owl during the winter, with a 43.26% of frequency and 69.12% of biomass. This contrast with the vast majority of the published research, where Microtus is the most frequent prey in North America (60.8% [1], 78-79% [11], 23.8% [15], 80-96% [3]), as well as Europe where it can comprise up to 99.7% of its diet [15]; however, Mus is the most important genus in Africa with up to 90.9% and Asia with a maximum of 77.4% [15]. In North America, Microtus has also shown the highest biomass (34-60% [16], 87-88% [11]).…”

“…From the rest of published studies, only three have mentioned this species and/or genus with a frequency lesser than 10% [17]. The vast majority of the studies found to be voles (Microtus) and especially M. pennsylvannicus the main long-eared owl prey in North America [1,3,11,15]. One of the reasons for this pattern is that Microtus species are not distributed in Janos-Casas Grandes area in Chihuahua [31], although there are records for the State of a relict subspecies (M. p. chihuahuensis [32,5]) that is now possibly extinct [10], and M. mexicanus that is distributed on higher elevations of the western part of Chihuahua [5].…”

“…The long-eared owl is a Holarctic species, distributed on the temperate regions of North America, Europe and Asia [1,2]. It inhabits dense vegetation, such as forests, riparian woodlands, and shrublands next to open areas used for low-height and ground foraging.…”

“…Its diet has been thoroughly studied, mostly in the United States and Europe, reporting to be over 90% based on rodents, mainly voles (Microtus spp. ), and to a lesser extent birds [1,3]. However, its feeding ecology on arid areas is far less known, especially during the winter.…”